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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Evgueni T. Filipov – Graduate Research Assistant , Department of Civil & Environmental Engineering (CEE), University of Illinois Jerome F. Hajjar – Professor, and Chair, CEE, Northeastern University Joshua S. Steelman – Graduate Research Assistant , CEE, University of Illinois Larry A. Fahnestock – Professor, CEE, University of Illinois James M. LaFave – Professor, CEE, University of Illinois Douglas A. Foutch – Professor Emeritus, CEE, University of Illinois 2011 ASCE SEI Structures Congress April 16, 2011 - Las Vegas, Nevada Illinois Department

• f Transportation

Illinois Center for Transportation

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Introduction

• IDOT Earthquake Resisting System (ERS):

 Recently developed & adopted design approach tailored to typical Illinois bridge types (and in part addressing increased hazard levels in AASHTO)  Primary objective: Prevention of span loss  Three levels of design and performance:

» Level 1: Connections between super- and sub-structures designed to provide a nominal fuse capacity » Level 2: Provide sufficient seat widths at substructures to allow for unrestrained superstructure motion » Level 3: Plastic deformations in substructure and foundation elements (where permitted)

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Quasi-Isolation for Bridges

• Typical bridge bearing systems designed to act as fuses to

limit the forces transmitted from the superstructure to the substructure

 Type I bearings: bearings with an elastomer to concrete sliding surface  Type II bearings: elastomeric bearings with PTFE sliding surface  L-shaped retainers: designed to limit service load deflections  Low-profile bearings with steel pintles and anchorbolts

04/14/2011 3 Elastomeric bearing on concrete Elastomeric bearing with PTFE sliding surface Low-profile fixed bearing

BRIDGE BEAM STEEL TOP PLATE TYPE I ELASTOMERIC BEARING WITH STEEL SHIMS RETAINER CONCRETE SUBSTRUCTURE ANCHOR BOLT

BRIDGE BEAM TOP PLATE WITH POLISHED STAINLESS STEEL SURFACE PTFE SURFACE CONCRETE SUBSTRUCTURE RETAINER ANCHOR BOLT TYPE II ELASTOMERIC BEARING WITH STEEL SHIMS BRIDGE BEAM PINTLE LOW-PROFILE FIXED BEARING ANCHOR BOLT CONCRETE SUBSTRUCTURE

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Bridge Prototype Model

• Three 50’ spans with six W27x84 Gr. 50 composite girders and

8” concrete deck

• 15’ Tall multi-column intermediate substructures
• Concrete abutments with backwalls and 2” gap from deck
• Pile foundations for all substructures

04/14/2011 4 Bridge Prototype Plan Mesh Representation of OpenSees Model Bridge Prototype Elevation

42'-0" 50'-0" 50'-0" 50'-0" 15'-0" LOW-PROFILE FIXED BEARINGS TYPE I - ISOLATION BEARINGS W27x84 ABUTMENT MULTI-COLUMN PIER

Type I - Bearings Low-profile fixed bearings

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Modeling of Bearing Components

• Sliding elastomeric bearing models

Ongoing experimentation is studying behavior Difference in static vs. kinetic coefficient of friction Friction slip-stick behavior noted in cases

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• 200
• 100

100 200

• 100
• 80
• 60
• 40
• 20

20 40 60

Displacement (mm) Force (kN) Bearing Type I; Exp.#5x1 Model:µSI=0.35; µSP=0.33; µK=0.24

50 100 150 200 10 20 30 40 50 60 70

Displacement (mm) Force (kN) Bearing Type I; Exp.#1 Model:µSI=0.37&µK=0.29 Bearing Type II; Exp.#9 Model:µSI=0.14&µK=0.06

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Bi-directional bearing elements

• Dependent on axial force
• Allows for initial capacity and different pre and post-slip

static coefficients of friction

• Force-displacement behavior coupled in orthogonal shear

directions

• Kinematic-hardening surface used to trace bearing

movement

04/14/2011 6 Combined Force Combined Displacement FK ΔINITIAL

BREAK

ΔSLIDE EINITIAL ΔFRIC

BREAK

FSI + FINITIAL

2 2 _1 _1 X Z

F F + FSP

2 2 _1 _1 X Z

∆ + ∆ EFRIC Z X

Static condition if (ΔX_1, ΔZ_1) is within dashed circle

ΔP_X_0 ΔX_0 ΔP_Z_0 ΔZ_0 ΔSLIDE ΔFRIC_BREAK θ0 θ1

(ΔX_1, ΔZ_1)

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

• Retainer simulation for

System Analyses

 Gap with elasto-plastic response until retainer fracture  Independent behavior of the (2) retainers  Calibrated based on experiments and Finite Element Modeling

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10 20 30 40 50 60 70 20 40 60 80 100 120 140 p Displacement (mm) Force (kN) Experiment # 7 Retainer Model

Modeling of Bearing Retainers

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Intermediate Substructures

• Beam-column elements with lumped plasticity

at nodes

• Fiber sections used to model nonlinear

behavior at hinge locations of column

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• 0.1
• 0.05

0.05 0.1

• 250
• 200
• 150
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• 50

50 100 150 200 250

Top Node Displacement (m) Force (KN)

Uncracked Cracked Elastic Cracked Inelastic

Column pier substructure with lumped plasticity at beam hinges Linear elastic pier cap Nodes for bearing attachment to substructure Linear elastic pile cap lp

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Foundations and Backwalls

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• 0.08
• 0.07
• 0.06
• 0.05
• 0.04
• 0.03
• 0.02
• 0.01

5000 Left Abutment Backwall Displacement (m) Force (KN) 5cm (2") Expansion Gap 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 5000 Right Abutment Backwall Displacement (m) Force (KN) 5cm (2") Expansion Gap Substructure Lateral Stiffness Rotational Stiffness Axial Stiffness 0” Springs to model local abutment foundation 5cm (2”) Gap Element Rigid Link representing backwall Zero length element allowing plastic hinge capability of backwall Hyperbolic Gap element with 0cm(0”) gap Node at bottom of bearing Zero length elements representing bearing and retainer connectivity Node for local abutment behavior Superstructure assembly Deck node

• Pile group analysis performed to

develop nonlinear force-displacement representation of foundations

• Hyperbolic gap material used to model

backwall interaction

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Limit State Identification Longitudinal

• Bearings

 Elastomer deformation & nonlinear behavior  Yielding and fracture in anchor bolts & pintles of fixed bearings  Sliding of bearings on substructure

• Column and wall piers

 Cracking of concrete  Yielding of reinforcement  Crushing of concrete

• Foundations

 Plastic deformation of backwall & backfill  Plastic deformation of pile groups & pile caps

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Longitudinal Analysis

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• Limit state identification stiff foundation
• 2500 yr Paducah ground motion

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Longitudinal Analysis

• Slip of bearings at abutments

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Longitudinal Analysis

• Yielding in substructure #2, backwall interaction, and plastic

deformation in foundation

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Longitudinal Analysis

• Slip of bearings at pier #1

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Limit State Identification Transverse

• Bearings

 Elastomer deformation, retainer deformation with fracture & nonlinear bearing behavior  Yielding and fracture in anchor bolts & pintles of fixed bearings  Sliding of bearings on substructure

• Column and wall piers

 Cracking and/or crushing of concrete  Yielding of reinforcement

• Foundations

 Plastic deformation of pile groups & pile caps  Possible interaction with backwall & backfill

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Transverse Analysis

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• Limit state identification fixed foundation
• 2500 yr Paducah ground motion (only 8 Seconds)

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Transverse Analysis

• Plasticity in retainers and bearing slip at abutment # 1

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Transverse Analysis

18

• Fracture of retainer component

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Transverse Analysis

19

• Fracture of fixed bearing

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

System Analyses Objectives

• Quantification of expected value and dispersion for:

Peak & residual bearing displacements Peak force demands on fuse components Peak force demands on sub-structures Sequence of fuse & systems failure

• Parametric study to investigate influence of:

Superstructure length and type Substructure height and type (column pier & wall) Isolation bearings (Type I & Type II) Foundation characteristics (stiff & soft soils)

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Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Summary & Conclusions

• New element models represent key aspects of local

bearing behaviors

• Global bridge model captures limit states for a

realistic three dimensional analysis

• Flexibility of elastomeric bearings and sliding of

bearings allows for quasi-isolated response

• Retainer elements and low-profile bearings need to

be carefully detailed to limit forces on substructures

• Backwalls have a significant contribution in limiting

longitudinal displacements

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